This invention relates to hysteresis machines and more specifically to a hysteresis machine having a rotor comprising a coil of amorphous metal tape which has been annealed to increase its coercivity.
Hysteresis machines, such as motors, are well known self-starting synchronous machines employing the hysteresis properties of the rotor. The driving force is provided by the rotating stator field which magnetizes the rotor. If the power supply frequency remains constant, rotor speed remains constant even if there are changes, within limits, in applied voltage, ambient temperature and attached torque load. Moreover, the motor speed is not affected by manufacturing variations, within predetermined limits. Consequently, the hysteresis synchronous machine can be used in virtually any application requiring synchronous motors.
Torque developed by the motor is proportional to area of the rotor material hysteresis loop, while exciting current for the motor is determined by coercive force of the rotor material. Thus, a coercive force should be selected for a particular hysteresis machine application which balances exciting current against the available torque for the machine.
The cost of hysteresis motor rotor material is several dollars per pound at the present time. Use of less expensive material for the hysteresis motor would be desirable. Amorphous metals have recently become available which have good magnetic properties and have a potential cost of one-tenth that of metals now used for hysteresis motors. Amorphous metals, however, are not available in a form convenient for manufacture of conventional laminated rotors. Thus the metal is in the form of a tape which is about 0.0005 to 0.003 inch thick and in widths of up to about 2 inches. The amorphous metal tape also has very low coercive force, of the order of from 0.01 to 0.1 oersteds.
Amorphous metal tapes having magnetic properties desired for application to electric machines are disclosed in U.S. Pat. Nos. 3,856,513, dated Dec. 24, 1974, in the name of Chen et al; 3,881,542, dated May 6, 1975, in the name of Polk et al; 4,052,201, dated Oct. 4, 1977, in the name of Polk et al; 4,059,441, dated Nov. 22, 1977, in the name of Ray et al. and 4,067,732, dated Jan. 10, 1978, in the name of Ray. A survey of metal glass technology is given in the article "Metallic Glasses" by John J. Gilman, appearing in Physics Today, May 1975, pages 46 to 53. Some attempts are being made to exploit the advantages of the properties of these metal tapes, for example, for acoustic devices as shown in U.S. Pat. No. 3,838,365.
An object of the present invention is to provide a low cost hysteresis machine which employs a coil of amorphous metal tapes as the rotor, the coil being annealed to substantially increase its coercive force.